Cancer and Its Cure. - Selective Toxicity of Anticancer Medicines

Running head: CANCER AND IT’S CURE
CANCER AND IT’S CURE
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a) SELECTIVE TOXICITY OF ANTICANCER MEDICINES
Selective Toxicity can be defined as the potential of a medicine or drug to recognize
the specific site in a microorganism or cell and inhibit its critical action on a living organism
(Biology LibreTexts, 2020). In this case, of anti-cancerous drugs, selective toxicity of a drug
is its ability to target cancerous cells at the specific site and inhibit its growth as well as
metastasizing capability that is, spread to other sites, and keeping the normal cells safe from
the action of toxic effects of the drug (Yun et al. 2015). The resistance grows when the cells
undergo different genetic changes thus, modifying the target sites on which the drugs acted
(Wei et al. 2015). There are quite a few mechanisms including selective toxicity. While
prescribing these drugs to the cancer patients, the dosage should also be decided after critical
thinking as it might exert various side effects, which includes the action of alkylating agents,
such as melphalan and cyclophosphamide that can destroy the cancer cells by inhibiting DNA
synthesis but also affects the bone marrow leading to leukaemia (Singh et al. 2015). There
are a few anticancer antibiotics as well which inhibits the DNA replication altogether but also
exerts a negative effect on the heart when prescribed in higher dosage (Agudelo et al. 2016).
The drugs which are tested on animal models in every aspect and ratio possible, when shows
positive results can be recommended to human (Salzano et al. 2015). However, one
significant advantage of selective toxicity is that it targets only the affected cells and does no
harm to healthy cells, which is essential for normal. Thus, it can be concluded that the ability
of selective toxicity to target specific targets sites is used in cancer therapy to inhibit the
cancerous cell growth and spread.
b) Limitations of Chemotherapy
Chemotherapy is an essential procedure of treating people with cancer and has proved
its efficiency over the time. There are a few positive points that make the usage of

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chemotherapy much advantageous as it can spread throughout the body destroying the cancer
cells. However, it has some disadvantages as well which include resistance towards the
treatment and many derogatory effects on the body (Wagner et al. 2017). The side effects
caused by chemotherapeutic agents vary among various types of cancer. Further side effects
include alopecia, vomiting, headache, fatigue, diarrhoea and might even lead to memory loss
in severe cases (Pearce et al. 2017). The cancerous cells in the body gradually develop
various mechanisms in which it can inhibit or bypass the action of chemotherapeutic drugs on
them. These mechanisms include the altering the target sites of the drugs, increase in the rate
of repairing the DNA replication altered by the drug, reducing the build-up or collection of
drug at a specific point and its increased exportation and avoiding the apoptosis or
programmed cell death mechanism (Wei et al. 2015). Chemotherapeutic drugs like antitumor
antibiotics, alkylating agents and antimetabolites exhibit quite a few limitations and leads to
side effects.
The antitumor antibiotics act by blocking the growth of cell by interfering with the
DNA. It also attack the cells during various phases of the cell cycle thus preventing the
uncontrolled cell division. Examples include anthracycline such as doxorubicine and
chromomycin. The mechanism of action of antitumor antibiotics occurs in three steps.
Initially, the drug interferes with the DNA replication and mRNA transcription by getting
intercalated within the DNA. Following this, the free radicals are generated by the action of
the antitumor antibiotics and the DNA strand gets broken. Lastly, the functions of DNA
Topoisomerase, an enzyme required to maintain the DNA replication is inhibited by the
antitumor antibiotic thus rendering the DNA non-functional (Zhang et al. 2016). There are
also a few limitations of using these antitumor antibiotics as it cause various critical effects
on human which includes vomiting, headache, fever, reduced white blood cell, red blood cell
and platelet count, damage of the neural system and the most important side effect of using

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this drug is it causes heart diseases and might lead to heart failure (Bhattacharya and
Mukherjee 2015). To overcome these side-effects, the patient can be recommended to check
temperature every day, decrease roughage and fiber, eating small & frequent meals, increase
fluids and take prescribed medications regularly.
Fig.1: Action of Doxorubicin. It is getting intercalated within the minor groove of DNA.
Free radicals such as superoxide ion generated and function of topoisomerase inhibited.
(Image retrieved from Meredith and Dass 2016)
Another class of drugs is of the alkylating agents, which prevent the cancer cells from
replicating by destroying the DNA. It can act at during any of the phases of cell cycle and
thus prevents the uncontrolled cell growth. For example, nitrogen mustard and busulfan. The
alkylating agents exhibit electrophilic behaviour by which it alkylates various nucleophiles
including the seventh nitrogen in guanine base of the DNA leading to the death of the cell
and proteins. The alkylation of DNA leads to various abnormal conditions in the DNA that
include abnormal base pairing of guanine with thymine, cross linking within the strand,
imidazole ring cleavage and depurination of the purine residue (Sing et al. 2018) However,
there are various limitations of using alkylating agents as the cure for cancer. The reasons are,
it causes toxicity of the bone marrow, toxicity of the mucosal system, toxicity of the neural